Engines may be configured with various fuel systems used to deliver a desired amount of fuel to an engine for combustion. One type of fuel system includes a port fuel injector and a direct fuel injector for each engine cylinder. The port fuel injectors may be operated to improve fuel vaporization and reduce engine emissions, as well as to reduce pumping losses & fuel consumption at low loads. The direct fuel injectors may be operated during higher load conditions to improve engine performance and fuel consumption at higher loads. Additionally, both port fuel injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery.
Engines operating with both port fuel injectors and direct injectors may operate for extended periods without using the direct injectors. The direct injectors may be coupled to a high-pressure fuel rail upstream of a high-pressure fuel pump. During periods of non-operation, a one-way check valve may result in high-pressure fuel being trapped in the high-pressure fuel rail. Any increase in temperature of the fuel would then result in an increased fuel pressure, due to the closed and rigid nature of the fuel rail. This increased temperature and pressure may in turn affect the durability of both the direct fuel injectors and the high-pressure fuel pump.
To reduce degradation of the direct fuel injectors and high-pressure fuel pump, a constant or periodic amount of fuel may be injected from the direct fuel injectors during operation of the vehicle. However, the inventors herein have recognized problems with such an approach. As one example, it may be desirable to run maximum sustained PFI operation for improved fuel economy and reduced emissions. In another example, the direct fuel injectors may be coupled to a limited supply of fuel, which may thus be depleted and not be available when needed if fuel is constantly injected. Further, this approach may not significantly impact component durability if fuel is injected below a threshold pressure or temperature over which the likelihood of degradation increases.
Such issues may be addressed by, in one example a method, comprising: operating an engine cylinder with fuel from a first injector and not a second injector and activating the second injector in response to a rail pressure increase of a fuel rail, the fuel rail coupled to the second injector. In this way, degradation of the second injector may be reduced by activating the second injector and allowing fuel flow through the second injector to reduce the pressure and temperature of the second fuel system components. Further, by monitoring rail pressure increases of a relative fixed-volume fuel rail, temperature changes corresponding to pressure changes can be identified so that relevant temperature information is obtained.
In another example, a fuel system for an internal combustion engine, comprising: a group of direct fuel injectors in communication with a group of cylinders, a first fuel rail in communication with the group of direct injectors, a high-pressure fuel pump in communication with the first fuel rail, and a control system configured with instructions for: during a first condition, increasing a flow of fuel through the first fuel rail when a temperature change in a fuel included in the first fuel rail exceeds a threshold, the temperature change based on a rail pressure change. In this way, if an engine is operating off a port-injection fuel system and not the direct injection fuel system, the direct injection fuel system may be activated even if not needed in order to cool the direct injection fuel system.
In yet another example, a method, comprising: operating an engine cylinder with fuel from a first injector and not a second injector, and activating a fuel pump coupled to the second injector in response to a rail pressure increase of a fuel rail, the fuel rail coupled between the second injector and the pump. In this way, fuel can be circulated through the fuel rail responsive to increases in rail pressure.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.